Hydraulic load cell with improved bridge-ring construction



July 19, 1966 D, E. GOLDING HYDRAULIC LOAD CELL WITH IMPROVED BRIDGE-RING CONSTRUCTION 2 Sheets-Sheet 1 Original Filed Sept. 18, 1963 y 19, 1965 D. E. GOLDING 3,261,41

HYDRAULIC LOAD CELL WITH IMPROVED BRIDGE-RING CONSTRUCTION Original Filed Sept. 18, 1963 2 Sheets-Sheet 2 Tlcyl- INVENTOR. 2A 141: 5 gab/- United States Patent F 3,261,417 HYDRAULIQ LOAD CELL WITH IMPRQVED BRIDGE-RING CONSTRUCTIGN David E. Golding, East Orange, N.J., assignor to Marcan Products Corporation, Greenwich, COK'IIL, a corporation of New York Continuation of abandoned application Ser. No. 309,775, Sept. 18, 1963. This application Apr. 14, 1965, Ser.

3 Claims. (Cl. 177-20s Another object is to provide a hydraulic load cell construction which is inherently capable of greater precision of load measurement than previous structures, and which is characterized by a substantial absence of mechanical hysteresis.

It is a specific object to meet the above objects with a structure of greater simplicity than heretofore and lending itself to greater reproducibility of precision performance, from one to the next cell manufactured to any given set of specifications.

Other objects and various further features of novelty and invention will be pointed out or will occur to those skilled in the art from a reading of the following specification in conjunction with the accompanying drawings. In said drawings, which show, for illustrative purposes only, preferred forms of the invention:

FIG. 1 is a vertical sectional view through a hydraulic load cell incorporating my invention;

FIG. 2 is an enlarged fragmentary plan view of the novel beam ring in the cell of FIG. 1;

FIG. 3 is a sectional view, taken along the line 33 of FIG. 2;

FIG. 4 is a further enlarged sectional view taken radially through a part of the ring of FIG. 2; and

FIG. 5 is a view similar to FIG. 4 to illustrate a modification.

Briefly stated, my invention is shown in application to a hydraulic load cell in which hydraulic fluid (e.g. automobile brake fluid) is trapped in a cavity beneath a flexible diaphragm. Load is applied to a column or piston member which covers substantially all but an outer annular part of the diaphragm, and it is this part which must be slightly flexed in the presence of a change in load. .My improvement resides in the construction of so-called beam ring means which bridges and supports this flexed annular part of the diaphragm, the construction incorporating means by which the beam ring is so fulcrumed on the piston and on a frame reference that complete symmetry of support is assured, with virtually a total lack of mechanical hysteresis.

Referring to FIG. 1 of the drawing, my invention is shown in application to a hydraulic load cell of the variety which is supported by a horizontal base which may be generally circular about a vertical axis of symmetry 11. The load to be measured is designated schematically by a heavy vertically downward arrow labeled F applied to a load platform 12, and this force is transmitted to a piston or column 13 overstanding a diaphragm 14 over a cavity 15 representing a trapped volume of hydraulic liquid beneath diaphragm 14 and within the base 10. Pressure indications are read by suitable indicating means 16 external to the cell and connected as suggested 3,261,417. Patented July 19, 1966 at 17 to suitable fittings 18 and passages 19-20-21 communicating with the cavity 15.

In the form shown, the base 10 is a heavy cylindrical slab formed with the passages 19-20-21 and defining an upstanding peripheral wall 22 having a flat surface to receive and seal with the diaphragm means 14 within the wall 22 a recess defining the cavity 15. This recess may extend for the full area within wall 22, but in the form shown, is annular, so that an upstanding central portion 23 may serve as a limit stop to prevent excessive displacement of the diaphragm 14.

To clamp the diaphragm 14 in place on the wall surface 22, a ring member 24 overstands the wall 22 and is secured by means of an angularly spaced plurality of bolts 25 extending at the bottom of the base 10 to the diaphragm and intothe ring 24. The ring 24 is of the elongated cylindrical variety so as to provide at the upper end of the cell a means for steadying the alignment of piston 13. Thus the upper end of ring 24 is secured to the outer limit of a stayplate 26 connecting the corre sponding other parts of the ring 24 and of the piston 13, spaced bolts 27 being shown to secure the stayplate to the piston 13 and bolts 28 being shown to secure the stayplate to the outer ring 24. The space between outer ring 24 and piston 13 is preferably substantial so that an opportunity may be afforded for the stayplate 26 to flex for the small vertical displacements of the piston that are involved in cell operation. This space between piston 13 and outer ring 24 may also be used to support an angularly spaced plurality of preload springs, schematically indicated at 29; springs 29 are supported between a ring 30 seated against a shoulder 31 in the piston 13 and a ring 32 secured to the outer ring 24 by the bolts 28 and by additional bolts 33. Bolt-s 28-33 are interlaced with each other at angularly spaced intervals, as will be understood. Annular clamp plates at 34-35 serve to more uniformly distribute the clamping pressures on the stayplate 26 over the outer ring 24 and the piston 13, respectively.

As previously indicated, load force F is applied to the piston 13 by way of a loading platform 12. In the form shown, slight horizontal misalignments between the cell base and the force application point are substantially reduced by providing a small degree of floating action in the connection between platform 12 and piston 13. This is achieved through what I term a vector ball 36 riding between concaved upper and lower seat inserts 37-38, fitting respectively in a socket or cavity 32 in the loading platform 12 and over a stud portion 40 at the top center of the piston 13. A boot 41 of rubber-like material is secured to both the loading platform 12 and the main outer ring 24 by means of circumferential clamps 42-43, thus making a unit-handling assembly.

At the lower end of the outer ring 24 and of the piston 13 corresponding opposed radially extending lips project at locations slightly offset from the plane of the diaphragm. On the outer ring 24 this lip is shown at 44 and for the piston 13 at 45, thus defining an annular space over the annular cavity 15, for which neither the outer ring 24 nor the piston 13 provides support. It is this part of the diaphragm which is subjected to the slight flexing involved in cell operation.

According to my invention, I materially improve the accuracy, precision and reliability of cell operation by employing a single beam ring construction to fill the flexed angular space between outer ring 24 and piston 13 and to support the diaphragm 14 over substantially this entire space. In FIG. 1, such a beam ring is designated 46 and it comprises a stiifly compliant essentially flat annular ring extending into preferably slight radial clearance relation with the outer ring 24 and the piston 13 but integrally incorporating a first fulcrum ridge d7 bearing against a lip 44 and a second fulcrum ridge 48 bearing against the piston lip 45. The ring 46 is preferably of high quality steel, as for example, saw stock, which is hardened so as to avoid peening. The lips 4 1-45 against which beam ring forces are applied in the presence of a heavy load are not constructed of such material, nor are they so hardened so that in the presence of a load there will be a slight peening or indentation of each of the lips 44-45 occasioned by penetration of the beam ring ridges 47-48. This penetration and peening eflect serves to keep the ridges 47-48 in the members with which they will always be associated. Once the penetration has been accomplished, the ring 46 is so located and will function freely.

In FIGS. 2, 3 and 4 I show in greater detail the beam or bridge ring construction just described in general terms. The ring 4-6 itself is as shown in FIG. 2, annular and substantially flat. In order that it may flex uniformly for its entire periphery, it is broken up into independent segments by means of a spaced plurality of radially inwardly open slots 49 interlaced with a similar plurality of radially outwardly open slots 59. The ring in FIG. 2 thus is defined by eighteen such segments due to the employment of nine inwardly open slots 49 and nine outwardly open slots 50. Referring to FIG. 4, the nature of each of the ridges 47-48 is such as to create a height above the central flat section 51 substantially of the same order of magnitude as the thickness of this flat portion. Also for each of the ridges 47-48 it :is preferred that their breadth and width dimensions be substantially the same and that the upper or crest surface for each of the ridges 47-48 be crowned as shown by employing a semi-circular formation. It will be understood that rocking action with minimum hysteresis is promoted for the ring segment associated with each of the independent flexible segments constituting the beam ring.

In FIG. 5 I show a modification applicable to extreme heavy duty load cells. The ring 46 of FIG. 5 may be slotted as described for the ring of FIGS. 2 to 4, but I prefer that it be continuously formed without slots, for greater strength. Also for greater strength, the central flat part 51' of the ring 46 has been given a much greater moment of inertia about a flex axis, thereby inherently supporting the diaphram with minimum beam ring bending at its central portion, and limiting the action of the beam ring to one of rocking between the two fulcrum locations, being at the ridges 52, for contact with the outer ring lips 44, and 53 for contact with the piston lip 45. The ring 46 is recessed or cut away at 54-55 in the region immediately adjacent each of the ridges 52-53 so as to provide clearance with the limits of the lips 44'-45' with which they are engaged.

It will be seen that I have described an improved bridgering construction featuring the fulcrumed support for the inner and outer edges of the ring, all as an integral part of the construction of the ring itself. It is thus possible to reproduce the performance of the cell, from one massproduced 'unit to the next, with a minimum of hysteresis eflects.

While I have described the invention in detail for the preferred forms shown, it will be understood that modifications may be made within the scope of the invention as defined in the claims which follow.

What is claimed is:

1. A hydraulic load cell, comprising a base including a circumferentially continuous upstanding wall with an upper peripheral seating surface and having a cavity for holding hydraulic fluid within said wall, diaphram means seated on said surface, hydraulic fluid filling the volume of said cavity beneath said diaphragm means, an outer ring member overstanding said wall and means securing said wall and ring and diaphragm to each other, said outer ring member having a circumferentially continuous lip offset from said diaphragm means and extending radially inwardly over a part of said cavity, a piston member on the inner part of said diaphragm means and in clearance relation with said outer ring member, said piston member having a circumferentially continuous lip offset from said diaphragm means and extending radially outwardly over part of said cavity and into adjacency with said outerring lip, and an annular bridge-ring member having a flat underside seated on said diaphragm means beneath both said lips, said bridge-ring member including at a radially outward location first circumferentially extending upwardly projecting ridge means integral with the body of said ring member in contact with the lower surface of said first lip, and at a radially inward location second circumferentially extending upwardly projecting ridge means integral with the body of said ring member in contact with the lower surface of said second lip, and said bridge-ring member including said ridge means being formed with a plurality of angularly space radial slots defining the ring as a succession of interconnected segments.

2. A hydraulic load cell according to claim 1, in which said bridge-ring member has a ring section characterized by an elongated fiat central portion, said radially inner and outer fulcrum-ridge projections extending upwardly thereof.

3. A hydraulic load cell according to claim 1, in which said bridge ring member has a ring section characterized by an elongated flat central portion tapering to reduced thickness toward radially inner and outer limits, said ridge means extending upwardly from the reduced parts of said tapered portions.

References Cited by the Examiner UNITED STATES PATENTS 2,561,321 7/1951 Tate 177208 X 2,960,328 11/1960 Tate 177-254 LOUIS I. CAPOZI, Primary Examiner.

LEO SMILOW, Examiner.

G. I. PORTER, R. S. WARD, Assistant Examiners. 

1. A HYDRAULIC LOAD CELL, COMPRISING A BASE INCLUDING A CRICUMFERENTIALLY CONTINUOUS UPSTANDING WALL WITH AN UPPER PERIPHERAL SEATING SURFACE AND HAVING A CAVITY FOR HOLDING HYDRAULIC FLUID WITHIN SAID WALL, DIAPHRAM MEANS SEATED ON SAID SURFACE, HYDRAULIC FLUID FILLING THE VOLUME OF SAID CAVITY BENEATH SAID DIAPHRAGM MEANS, AN OUTER RING MEMBER OVERSTANDING SAID WALL AND MEANS SECURING SAID WALL AND RING AND DIAPHRAGM TO EACH OTHER, SAID OUTER RING MEMBER HAVING A CIRCUMFERENTIALY CONTINUOUS LIP OFFSET FROM SAID DIAPHRAGM MEANS AND EXTENDING RADIALLY INWARDLY OVER A PART OF SAID CAVITY, A PISTON MEMBER ON THE INNER PART OF SAID DIAPHRAGM MEANS AND IN CLEARANCE RELATION WITH SAID OUTER RING MEMBER, SAID PISTON MEMBER HAVING A CIRCUMFERENTIALLY CONTINUOUS LIP OFFSET FROM SAID DIAPHGRAM MEANS AND EXTENDING RADIALLY OUTWARDLY OVER PART OF SAID CAVITY AND INTO ADJACENCY WITH SAID OUTERRING LIP, AND AN ANNULAR BRIDGE-RING MEMBER HAVING A FLAT UNDERSIDE SEATED ON SAID DIAPHRAGM MEANS BENEATH 